Paramagnetic centers in single-walled carbon nanotubes encapsulated with palladium and their interaction with hydrogen at H/C ≥ 1.0

The nature of paramagnetic centers in a nanostructure based on single-walled carbon nanotubes (SWCNTs) encapsulated with Pd was studied by EPR spectroscopy at 77 and 293 K. It was found that strong charge-transfer π complexes of the (Pd-C _x ) type, which manifested themselves as a narrow resonance (ΔH = 6–8 G and g = 2.002 at T = 77 k), were formed in the Pd-SWCNT composite along with impurity centers (Fe₃O₄ nanoparticles within the nanotubes), which were responsible for a broad EPR signal (ΔH = 75 G and g = 2.065 at T = 293 K). These complexes were found to be predominant adsorption sites responsible for a high gravimetric density of hydrogen (H/C ≥ 1.0) within the single-walled carbon nanotubes.